=The Motions of the Moon.=—The Moon turns round on its axis once every month and it also revolves round the Earth once every month, so that the Moon’s day and year are of the same length just like Mercury and Venus, and this is the reason that one side of the Moon is always turned toward the Earth, as you will see if you look at her through a glass. [Illustration: FIG. 107.—THE EXPERIMENT SHOWING HOW ONE REVOLUTION OF THE MOON ROUND THE EARTH MAKES IT TURN ONCE ROUND ITS AXIS.] A simple experiment will show the cause of this: Place an apple, which we will call the Earth, on the bottom of an inverted glass on a table, and draw a chalk circle a foot in diameter around it. Next, take a tablespoon to represent the Moon, and hold it upright with the point of its bowl on the chalk line and with the bowl turned toward the apple, as shown in Fig. 107. Now, draw the spoon round the circle, turning it in your fingers so that the bowl is always toward the apple. It is easy to see that in order for the bowl of the spoon to be turned toward the apple during all of its travels round the chalk circle the spoon must also turn once round on its own axis, and this is the reason we always see the same side of the Moon. =The Moon’s Phases.=—Since one side of the Moon is always turned toward the Earth, it is clear that this is the only side we can ever see, and, further, we are only able to see as much of this side as is made bright by the Sun’s light. [Illustration: FIG. 108.—APPLE CUT TO SHOW CRESCENT.] The different _aspects_ we get of the Moon as it revolves round the Earth are called the _Moon’s phases_; and each phase has a name, as the _new moon_; the _first quarter_; the _full moon_, and the _last quarter_. Between the new Moon and the first quarter, and between the last quarter and the new Moon only a crescent, or sickle-like edge of the Moon, can be seen; while between the full Moon and last quarter the Moon is gibbous (pronounced gib´-us and meaning swelled, or shaped like a football). If you will look at the picture, Fig. 108, and the diagrams, Figs. 109 and 110, and do the experiment which follows, the way the phases of the Moon are made will be perfectly clear. The picture, Fig. 108, shows an apple from which a thin _sector_ or slice has been cut. The lower picture shows the stem end of the apple and from this point of view the part where the slice was cut out looks wedge-shaped. This is the view of the Moon shown in Fig. 109, if we could look down on it. [Illustration: FIG. 109.—DIAGRAM SHOWING HOW THE MOON’S PHASES ARE MADE.] Now turn the apple on its side and the place where the slice was cut out can be seen from the stem to the blossom end of the apple when it takes on a crescent form. This is the view of the Moon we really get between new Moon and its first quarter, as shown in Fig. 110.